InvNo Amount -------------------- 0001 120.00 0002 40.00 0001 15.00 0001 10.00 0002 20.00GROUP BY will usually be used with a function such as SUM(). For example, if what you want is the total for each invoice,
SELECT InvNo, SUM(Amount) AS Total FROM InvDetail GROUP BY InvNo
would return:InvNo Total
----------------
0001 145.00
0002 60.00
I hope this clears things up a little!